Candidatus Dactylopiibacterium carminicum, a Nitrogen-Fixing Symbiont of Dactylopius Cochineal Insects (Hemiptera: Coccoidea: Dactylopiidae)

Abstract

The domesticated carmine cochineal Dactylopius coccus (scale insect) has commercial value and has been used for more than 500 years for natural red pigment production. Besides the domesticated cochineal, other wild Dactylopius species such as Dactylopius opuntiae are found in the Americas, all feeding on nutrient poor sap from native cacti. To compensate nutritional deficiencies, many insects harbor symbiotic bacteria which provide essential amino acids or vitamins to their hosts. Here, we characterized a symbiont from the carmine cochineal insects, Candidatus Dactylopiibacterium carminicum (betaproteobacterium, Rhodocyclaceae family) and found it in D. coccus and in D. opuntiae ovaries by fluorescent in situ hybridization, suggesting maternal inheritance. Bacterial genomes recovered from metagenomic data derived from whole insects or tissues both from D. coccus and from D. opuntiae were around 3.6 Mb in size. Phylogenomics showed that dactylopiibacteria constituted a closely related clade neighbor to nitrogen fixing bacteria from soil or from various plants including rice and other grass endophytes. Metabolic capabilities were inferred from genomic analyses, showing a complete operon for nitrogen fixation, biosynthesis of amino acids and vitamins and putative traits of anaerobic or microoxic metabolism as well as genes for plant interaction. Dactylopiibacterium nif gene expression and acetylene reduction activity detecting nitrogen fixation were evidenced in D. coccus hemolymph and ovaries, in congruence with the endosymbiont fluorescent in situ hybridization location. Dactylopiibacterium symbionts may compensate for the nitrogen deficiency in the cochineal diet. In addition, this symbiont may provide essential amino acids, recycle uric acid, and increase the cochineal life span.

Cophylogenetic analysis suggests cospeciation between the Scorpion Mycoplasma Clade symbionts and their hosts

“…In addition, bacterial symbionts offer protection against natural enemies such as pathogenic fungi [12,13], viruses [14], predators [15], parasitoids [16][17][18], and parasitic nematodes [19]. In some insects such as termites, bark beetles and in the carmine cochineals there are nitrogen-fixing bacteria that compensate low nitrogen diets [20][21][22].…”

Metatranscriptomic Analysis of the Bacterial Symbiont Dactylopiibacterium carminicum from the Carmine Cochineal Dactylopius coccus (Hemiptera: Coccoidea: Dactylopiidae)

“…Notably, the cochineals Dactylopius spp. do not contain flavobacterial endosymbionts or bacteriomes (special organs with insect cells that contain bacterial endosymbionts), as other scale insects do; they instead harbor a betaproteobacterium named Candidatus Dactylopiibacterium carminicum (hereafter abbreviated as Dactylopiibacterium ), two strains of Wolbachia ( w DacA and w DacB), and a Spiroplasma [16,17], in addition to various fungi [18]. Other bacteria that have been sporadically found may represent transient gut bacteria that were acquired from the host plant [19].…”

“…Dactylopiibacterium was detected in all tested individuals from the domesticated D. coccus , from the wild species Dactylopius ceylonicus , D. confusus , D. opuntiae , and D. tomentosus [17], and in the ovaries of D. coccus and D. opuntiae [19]. The genomes of Dactylopiibacterium recovered from the metagenomes from females and males of D. coccus , as well as those recovered from the wild species D. opuntiae were published [17]. Due to their large genome, Dactylopiibacterium seems to be a recently acquired cochineal symbiont [17].…”

What do we know about biological nitrogen fixation in insects? Evidence and implications for the insect and the ecosystem

“…Rather, it indicates the presence of such bacteria in representatives of multiple insect orders, including Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Thysanoptera, which feed on varied diets, such as bark, dung, fruits, honey dew, sap, leaves, and seeds. This list is likely to be an underestimation of the actual distribution of potential diazotrophs in insects, as new associations are continuously being reported, for example, in Euoniticellus dung beetles (Shukla et al ., ) and in Dactylopius cochineal insects (Vera‐Ponce de León et al ., ). In addition, studies of insect microbiomes that detected potential diazotrophs but did not discuss them in this context were not likely to be gathered by our survey.…”